1. Field of the Invention
This invention relates to ventilation systems, more particularly to roof ventilation systems that help to protect buildings against fires.
2. Description of the Related Art
Ventilation of a building has numerous benefits for both the building and its occupants. For example, ventilation of an attic space can prevent the attic's temperature from rising to undesirable levels, which also reduces the cost of cooling the interior living space of the building. In addition, increased ventilation in an attic space tends to reduce the humidity within the attic, which can prolong the life of lumber used in the building's framing and elsewhere by diminishing the incidence of mold and dry-rot. Moreover, ventilation promotes a more healthful environment for residents of the building by encouraging the introduction of fresh, outside air. Also, building codes and local ordinances typically require ventilation and dictate the amount of required ventilation. Most jurisdictions require a certain amount of “net free ventilating area,” which is a well-known and widely used measure of ventilation.
An important type of ventilation is Above Sheathing Ventilation (“ASV”), which is ventilation of an area within a roof above the sheathing on a roof deck, such as in a batten cavity between the top of the roof deck and the underside of the tiles. Increasing ASV has the beneficial effect of cooling the batten cavity and reducing the amount of radiant heat that can transfer into the structure of the building, such as an attic space. By reducing the transfer of radiant heat into the building, the structure can stay cooler and require less energy for cooling (e.g., via air conditioners).
In many areas, buildings are at risk of exposure to wildfires. Wildfires can generate firebrands, or burning embers, as a byproduct of the combustion of materials in a wildfire. These embers can travel, airborne, up to one mile or more from the initial location of the wildfire, which increases the severity and scope of the wildfire. One way wildfires can damage buildings is when embers from the fire land either on or near a building. Likewise, burning structures produce embers, which can also travel along air currents to locations removed from the burning structures and pose hazards similar to embers from wildfires. Embers can ignite surrounding vegetation and/or building materials that are not fire-resistant. Additionally, embers can enter the building through foundation vents, under-eave vents, soffit vents, gable end vents, and dormer or other types of traditional roof field vents. Embers that enter the structure can encounter combustible materials and set fire to the building. Fires also generate flames, which can likewise set fire to or otherwise damage buildings when they enter the building's interior through vents.